This invention relates to a cutting, drilling or wear-resistant tool comprising a tool substrate and a hard sintered body of diamond or cubic boron nitride bonded to the tool substrate with high strength and rigidity, and a method of manufacturing the same.
Sintered diamond manufactured by sintering fine diamond particles using a binder such as an iron-family metal in ultra-high-pressure, high-temperature environments, has far higher wear resistance than conventional cemented carbides, and is thus widely used as a material for cutting edges of cutting tools, wire-drawing dies, drill bits and wear-resistant tools. A sintered material made by sintering fine cubic boron nitride particles using various binders shows excellent performance when used for cutting hard iron-family metals and cast iron.
FIG. 5 shows a conventional cutting tool having a hard sintered body bonded. A hard sintered body 1 is manufactured as a composite sintered body of diamond or cubic boron nitride lined with a support 2 of cemented carbide. This hard sintered body has its side of the support 2 brazed to a tool substrate 4 through a bonding layer 3 mainly of Ag or Cu to form a cutting tool as shown in FIG. 5.
During brazing, these composite sintered bodies are subjected to quick heating and cooling. Thus, according to conditions, cracks and breakage may occur at the bond interface between the hard sintered body 1 and the support 2 of cemented carbide due to a difference in thermal expansion between these materials. Further, even after the cutting tool has been completed, according to the sintering conditions of the hard sintered body, due to low bond strength at the interface, under severe cutting conditions, peeling or chipping may occur during cutting. Thus, there was a problem in reliability of the tool.
In order to overcome these problems, unexamined Japanese patent publication 60-85940 proposes to improve the reliability at the interface by forming a carbide or nitride of Ti or Zr at the interface between the sintered body and the support of cemented carbide. But since the composite sintered bodies are formed by bonding different materials that are different in thermal expansion, the effect of improvement was limited.
On the other hand, it has been contemplated to bond the hard sintered body 1 (of diamond or cubic boron nitride) to the tool substrate 4 not through the support 2 cemented carbide but directly to eliminate the bond interface between the hard sintered body 1 and the support 2 of cemented carbide. Such tool structures are disclosed in unexamined Japanese patent publications 59-134665 and 60-187603, examined Japanese utility model publication 64-4839,1 unexamined Japanese patent publication 2-274405, examined Japanese patent publication 3-17791, and unexamined Japanese patent publications 7-124804 and 9-108912. These prior art publications disclose that an active metal layer is formed on the surface of a diamond sintered body or a cubic boron nitride sintered body, and it is bonded directly to a tool substrate by a brazing filler made mainly of Ag or Cu, or using an active brazing filler comprising a soft metal such as Ag, Cu or Au and an active metal such as Ti, zr or Ta, such as Ag--Cu--Ti, Cu--Ti, Ag--Ti, Au--Ta or Au--Nb.
In these prior arts, since a sintered body of diamond or cubic boron nitride is bonded to a tool substrate through a bonding layer made mainly of a soft metal such as Ag, under severe cutting conditions, there were various problems such as lowering of the cutting accuracy or worsening of the surface roughness due to deformation of the bonding layer, chattering due to lack of rigidity, and erosion of the brazing material and breakage of the tool due to the fact that cutting heat produced at the tool cutting edge flows directly into the bonding layer through the sintered body which has a high thermal conductivity.
An object of the present invention is to provide a hard sintered body tool in which a hard sintered body of diamond or cubic boron nitride is bonded to a tool substrate through a bonding layer with high strength and rigidity such that the hard sintered body will not break or crack.
An object of this invention is to prevent cracks and breakage of the hard sintered body when brazed while achieving high bond strength between the sintered body and the tool body.